1. Field of the Invention
This invention relates to field emission devices, and particularly to amplifier and oscillator devices which rely on field emission.
2. Description of Related Art
Although high-power microwave and millimeter-wave circuits having invariably involved the use of thermionic vacuum devices, most low-power high-frequency devices are now formed by conventional solid state techniques.
Transit time induced limitation of high frequency performance in vacuum electronic devices can usually be made negligibly small because of the ballistic electron motion in a vacuum. However, just as in solid state devices, the ultimate speed of operation of a vacuum device is likely to be capacitance limited. In conventional large-scale vacuum electronic devices, a number of particular designs have been developed to overcome this limitation. These designs involve some combination of velocity modulation and distributed amplification.
The combination of velocity modulation and a relatively long drift space can result in a spatial separation of fast and slow electrons. The bunching of electrons occurring as faster electrons overtake slower electrons emitted earlier can produce an approximately 50% modulation of the current at the frequency of a small modulating signal applied thereto. This forms the operational basis of the klystron. The main limitations to the gain available from such device are the energy spread of the electron beam prior to modulation and control of the momentum of the electrons both before and after modulation.